Some triple negative breast cancers are dependent on utilization of glutamine for survival and proliferation. Glutamine-addictive phenotype provides a potential therapeutic target and may lead to more effective management of triple negative cancers, which currently have few therapeutic options. Considering the heterogeneity in gene expression profile and possibly glutamine utilization in these cancers, a non- invasive imaging marker that would identify the glutamine-avid phenotype is necessary. Based on promising preliminary data from animal studies of a newly developed 18F- labeled glutamine analog for positron emission tomography (PET), this R21 proposal will examine key feasibility issues of this imaging probe. We will determine the nature of probe uptake, its dependence on transport systems and glutaminase activity. Completion of the R21will determine whether this PET glutamine tracer can discriminate triple negative breast cancers based on the glutaminolysis level, and whether clinical translation of this PET tracer is warranted for use as a predictive biomarker for therapies targeting glutamine metabolism.